An analog to digital converter (“ADC”) converts an analog signal into a digital representation of the analog signal. The ADC typically samples the analog signal at periodic intervals and generates a digital value for each sample indicating the approximate magnitude of the sampled analog signal.
One type of ADC uses a technique known as successive approximation (“SAR”) to convert each analog input sample to a digital value. This type of ADC typically includes a digital to analog converter (DAC) and a single comparator to produce a digital value representing the magnitude of the analog input sample. The DAC is used to produce a reference voltage based upon a digital input value. The comparator is used to compare the DAC output to the analog input sample. The ADC converts an analog input sample to a digital value by successively changing the DAC output and comparing the DAC output to the analog input sample.
The DAC may consist of a binary weighted capacitor array. In an ideal DAC, each of the capacitors associated with a particular bit position is one-half the capacitance of the capacitor associated with the previous bit position, although such a configuration is not economically feasible to implement in practice.
It is sometimes necessary to sample multiple analog inputs simultaneously. This can be useful for maintaining the phase information of the analog inputs. Thus far previous inventions have attempted to sample N inputs using N ADCs. Accordingly, there is a need in the art for an efficient scheme for implementing N simultaneous sampling analog to digital converter using N sample and holds and a single ADC.